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HMC739 VCO and HMC733 Mixer output is lower than expected

I am using the HMC739 and setting the VTUNE to 2 is to get 24GHz.  I have the output of this going to the mixer.  The mixer is mixing in a signal and is send to an SMA connector that I have an antenna attached to.

According to the HMC datasheet of the HMC739, I should expect a 11dBm 24GHz signal (or close to it) go into the mixer.

According to the HMC733 datasheet it has a 9dBm insertion lose, so I should expect a 3dBm signal out the transmit antenna.  

I seem to be getting a -22dBm signal instead of the 3dBm one.  Have you seen this before?  Any idea what would cause such a loss?

Thanks,

Rich

  • Hi Rich, 

    Not too much to go on here (no schematic, photos of setup...) so here's what I've got based on what you've given me. 

    Sounds like you're using this for up conversion but you didn't state which port the HMC739 is on (I assume LO). What is on the RF port and what is the drive level there? What is your IF freq? 

    Have you confirmed that you are getting +5 VDC on pin 20 of the HMC739 and it's drawing about 200 mA? (assumes Vcc (Dig) also being used) Do you measure +11 dBm out of the HMC739? The datasheets de-embed the board loss so the actual power at the connector may be slightly lower and there will be some additional board loss at the input of the mixer. If there are cable and adapters involved these also add insertion loss and depending on their quality, impedance mismatch. The insertion loss of the boards alone could easily drop the actual drive level at the input of the mixer to 9 dBm at 24 GHz

    At a +9 dBm drive level, IP3 at 24 GHz is reduced to about +13dBm (from +23and conversion loss increases to about -12 dBm. 

    At 24 GHz a poorly soldered cap or connector could easily attenuate your signal. By the way, I think you may mean the HMC773  passive mixer (733 is a wideband VCO). 

    I recommend measuring the power out of the mixer IF port directly to better understand the drive level into the antennae. 

    If all this checks out attach some photos and schematic and I'll see what else I can do to help. 

    Best regards, 

    Marty